Anyone following the debate about climate change over the last few years might be forgiven for feeling a little cast down. The pessimists, it seems, have the most compelling arguments, and no shortage of persuasive-looking evidence to support the gloomiest of prognoses. So if something even vaguely optimism-inducing comes along, we ought to at least give it the benefit of the doubt.

The most positive news to come out of the United States for a long time was US president Barack Obama’s recent declaration that by 2030 he was going to cut carbon dioxide emissions from power stations by 30%. If realised, this could have a potentially enormous tangible and symbolic impact. Not only would there be a very real and substantial reduction of planet-warming carbon dioxide, but such a unilateral action could have a galvanising effect on other states.

Until very recently the US was responsible for the largest share of carbon dioxide emissions and other states – such as Australia – could argue with some justification that if the US didn’t act there was no point in them bothering either.

Whether you buy that argument or not, it is potentially invalidated by Obama’s proposal. If one of the biggest contributors is actually trying to address the quintessential collective action problem confronting humanity, the moral imperative for joining in arguably becomes more compelling.

I say ‘arguably’ because the harder-headed – some might say bone-headed – amongst us are unlikely to be won over by such reasoning. Dealing with free riders within the confines of national borders is difficult enough; there are simply no precedents for it internationally. Despair seems entirely reasonable in such circumstances – but not just yet, perhaps.

The comparatively good news is that there are other reasons for acting that rely less on altruism or a sense of common humanity. Realists don’t get much more calculating or instrumental than they do in China, and yet in the People’s Republic, too, addressing climate change is one of the country’s top priorities.

It’s not hard to see why: parts of the country are becoming quite literally unliveable and China’s expanding middle classes are taking to social media and – even more alarmingly from the ruling elite’s perspective – the streets to express their unhappiness.

The pressure on Xi Jinping and the rest of the ‘communist’ leadership is consequently growing and threatening to undercut the already fragile legitimacy of the state in China. But authoritarian leaders enjoy one great advantage that their democratic counterparts do not: in extremis, Xi can compel compliance in a way Obama cannot.

Coincidentally, China has also set a target of 30% reduction for the emissions intensity of key industries. China is currently the world’s largest consumer of cheap and plentiful coal – much of it from Australia – so this is not only a technically challenging problem, but one that is likely to have serious short-term economic impacts.

In the long-term, a mandated shift from coal to renewable energy may actually give Chinese companies an important lead in the technologies of the future. But in the long-term, as Keynes famously pointed out, we’re all dead. Political cycles can be brutally short and hopelessly out of kilter with the relatively long-term nature of climate change.

But if this is a problem for China, it is doubly so for the US. Is it any coincidence that Obama has left it until nearly the end of his presidential term, when thoughts turn to the all important ‘legacy’, before deciding to act?

Yet even when freed from the constraints of a possible electoral backlash, effective action will prove difficult. Significantly, Obama has chosen to use the existing Clean Air Act to bypass Congress where the coal industry and its supporters exert such influence.

If the principal obstacles to action in China are technical and organisational, in the US they are political and economic. It is far from clear which, if either, of these systems is best equipped to address a problem that is unprecedented in scale and complexity. The answer will be of interest to more than just students of comparative public policy.

Paradoxically enough, the area that may seem the most intractable – international co-operation to tackle climate change – currently looks slightly more promising. Recent high level talks between China and the US about possible cooperative approaches to a common problem provide grounds for at least cautious optimism.

Everyone knows that collective action is required even to begin addressing climate change. It is also clear that nothing will happen without the US and China playing key roles. Environmental cooperation could provide both countries with a politically useful circuit-breaker at a time of growing international tension. Collective leadership from the G2? Hope springs eternal.